1. Field of the Invention
The present invention relates to an optical heads device and the like used in an optical disk device and the like for reproducing or recording information from and to an optical recording medium such as an optical disk and the like. In particular, it relates to an optical heads device capable of reproducing or recording information for two or more types of optical disks different from each other.
2. Related Art of the Invention
In general, to increase recording capacity in an optical disk device, it is necessary either to reduce the wavelength of a laser light used for recording and reproduction of information on an optical disk, which is an optical recording medium, or to increase the numerical aperture (NA) of an objective lens for focusing the laser light onto the optical disk, so that recording density of the optical disk is increased.
In recent years, in the optical head used for the optical disk device, for example, the numerical aperture of the objective lens for CD (Compact Disc) has become 0.45, and the numeral aperture of the objective lens for DVD (Digital Versatile Disc) has become 0.6, and moreover, since an effective diameter itself of the objective lens has become small due to reduction in size of the optical head, a so-called working distance (WD) between the top end of the objective lens and the surface of the optical disk has been reduced, thereby increasing the possibility that the objective lens ends up coming into collision with the surface of the optical disk in contrast to a conventional lens.
Further, in the case of CD, while the thickness of a transparent substrate is 1.2 mm, in the case of DVD, it is 0.6 mm and thin, and the distance to an information recording layer protected by the transparent substrate is shortened. Hence, scars caused on the surface of the optical disk by the collision of the objective lens greatly affect signals.
Further, with the advent of a rewritable DVD such as DVD-RAM (Digital Versatile Disc-Random Access Memory) and the like, it has become possible for the user to perform a recording on the optical disk, and therefore, serious consequence has been often developed by the scars of the surface of the optical disk and this has necessitated the reduction of the collision between the objective lens and the surface of the optical disk.
Moreover, in recent years, a recordable superdense optical disk with a blue-violet laser as a light source (Blu-ray Disc, numerical aperture of the objective lens 0.85, thickness of the transparent substrate 0.1 mm) has been also developed, and in such a superdense optical disk of a thin film substrate, a collision-avoidance function for avoiding the collision between the objective lens and the optical disk has become indispensable by now.
In the meantime, in this kind of the circumstance where there exist plural types of optical disks, an optical disk device which can reproduce or record both of a conventional optical disk (for example, CD and DVD) and a new optical disk (for example, Blu-ray Disc) is commonly desired. Under such circumstance, a number of optical disk devices capable of reproducing or recording plural types of optical disks have been proposed, and for example, an optical heads device that selects plural objective lenses and performs reproduction or recording of information for the plural types of optical disks different in the thickness of a disk substrate has been proposed.
In FIG. 9 is shown a schematic block diagram of the optical heads device for selecting the objective lens and performing the reproduction or recording of information. In FIG. 9, reference numeral 101 denotes a semiconductor laser for emitting a laser light of a wavelength of 650 nm, reference numeral 102 abeam splitter, reference numeral 103 a ¼ wavelength plate, reference numeral 104 a collimator lens, reference numeral 105 a reflecting mirror, reference numeral 106 an objective lens, reference numeral 107 an anamorphic lens, reference numeral 108 a photosensing element, and reference numeral 109 a biaxial actuator corresponding to a first objective lens driving means, and these constitute a first optical system 110 as a first optical head.
Similarly, reference numeral 111 denotes a photosensing and light emitting integrated element in which the semiconductor laser for emitting a laser light of a wavelength of 780 nm and the photosensing element are integrated, reference numeral 112 a polarization hologram, reference numeral 113 a ¼ wavelength plate, reference numeral 114 a collimator lens, reference numeral 115 a reflecting mirror, reference numeral 116 an objective lens, and reference numeral 119 a biaxial actuator corresponding to a second objective lens driving means, and these constitute a second optical system 120 as a second optical head.
Further, reference numeral 130 denotes a first optical disk having a transparent substrate of 0.6 mm in thickness, and reference numeral 140 denotes a second optical disk having a transparent substrate of 1.2 mm in thickness. While, in FIG. 9, the first optical disk 130 and the second optical disk 140 are shown to be superposed, in reality, either one only of the optical disks is inserted into a drive (not shown).
The operation in case of performing the reproduction or recording for the first optical disk 130 will be described.
The laser light of a linear polarized light having a wavelength of 650 nm emitted from the semiconductor laser 101 transmits the beam splitter 102, and is converted into a circularly polarized light at the ¼ wavelength plate 103, and after that, is converted into a parallel light at the collimator lens 104, and is reflected at the reflecting mirror 105, and is converged into an information recording layer of the first optical disk 130 as a light spot by the objective lens 106 across the transparent substrate of 0.6 mm in thickness. The laser light reflected at the first optical disk 130 transmits again the objective lens 106, and is reflected at the reflecting mirror 105, and transmits the collimator lens 104, and is converted into a linearly polarized light different from an outward route at the ¼ wavelength plate 103, and after that, it is reflected at the beam splitter 102, and is led to the photosensing element 108 by the anamorphic lens 107.
The laser light detected by the photosensing element 108 is subjected to photoelectric conversion, and after that, it is arithmetically operated, and generates a focusing error signal for following a surface deviation of the first optical disk 130 and a tracking error signal for following a decentering. The biaxial actuator 109 drives the objective lens 106 in a biaxial direction by these focusing error and tracking error signals, so that the light spot follows an information track of the first optical disk 130 in a rotation state.
Similarly, the operation in case of performing the reproduction or recording for the second optical disk 140 will be described.
The laser light of a linear polarized light having a wavelength of 780 nm emitted from the semiconductor laser inside the photosensing and light emitting integrated element 111 transmits the polarization hologram 112, and is converted into a circularly polarized light at the ¼ wavelength plate 113, and after that, it is converted into a parallel light by the collimator lens 114, and is reflected at the reflecting mirror 115, and is converged into an information recording layer of the second optical disk 140 as a light spot by the objective lens 116 across the transparent substrate having a thickness of 1.2 mm. The laser light reflected at the second optical disk 140 transmits again the objective lens 116, and is reflected at the reflecting mirror 115, and transmits the collimator lens 114, and is converted into a linear polarized light different from the outward route by the ¼ wavelength plate 113, and after that, it is guided to the photosensing element inside the photosensing and light emitting integrated element 111 by the polarization hologram 112.
The laser light detected by the photosensing element inside the photosensing and light emitting integrated element 111 is arithmetically operated after photoelectric conversion, and generates the focusing error signal for following the surface deviation of the second optical disk 140 and the tracking error signal for following the decentering. The biaxial actuator 119 drives the objective lens 116 in the biaxial direction by these focusing error and tracking error signals, so that the light spot follows an information track of the second optical disk 140 in a rotation state.
FIG. 10 schematically shows the configuration of a biaxial actuator 109. The biaxial actuator 119 has the same configuration. In FIG. 10, reference numeral 106 denotes an objective lens, reference numeral 191 a lens holder, reference numeral 192 a suspension wire, reference numeral 193 a fixing unit, reference numeral 194 a coil, reference numeral 195 a magnetic yoke, and reference numeral 196 a magnet.
The lens holder 191 is fixed to one end of four suspension wires 192, and moreover, the focusing and tracking coils 194 are fixed to it.
These coils 194 are arranged in opposite to a magnetic circuit constituted by the magnetic yoke 195 and the magnet 196. The lens holder 191, the objective lens 106, and the coil 194 are integrally formed and constitute a movable unit. In these configurations, the movable portion is movably supported in a focusing direction and a tracking direction, and the position of the objective lens 106 can be controlled in a biaxial direction by the current flown through the coil 194.
Since the biaxial actuator to support the movable portion by the four suspension wires in this way is highly efficient and excellent in miniaturization and cost reduction, it is widely used as an optical head biaxial actuator.
Next, as the optical head comprising a conventional collision avoidance function, there has been known an optical head described in Japanese Patent Application Laid-Open No. 2002-237071. In FIG. 11 is shown a schematic block diagram of the objective lens comprising a conventional collision avoidance mechanism. In FIG. 11, reference numeral 201 denotes an objective lens, reference numeral 202 a lens barrel for supporting the objective lens, reference numeral 203 an effective diameter portion (hereinafter referred to also as lens effective surface) in the light emitting surface of the objective lens, reference numeral 204 a collision avoidance unit, and reference numeral 205 an optical disk.
The collision avoidance unit 204, which is a buffer layer, contacts the optical disk 205 prior to the lens effective surface 203 of the objective lens 201. The collision avoidance unit 204 is circularly formed on the surface of the objective lens 201 by resin, and an aperture diameter of the collision avoidance unit 204 is larger than the diameter of the lens effective surface 203. As a resin material, an ultraviolet curing resin softer than the material of the surface of the optical disk 205 can be also selected.
As shown in FIG. 11, the collision avoidance unit 204 is adhered to the inner surface of the lens barrel 202 supported by its peripheral side surface. Further, the collision avoidance unit 204 protrudes to the optical disk 205 side from the end surface of the lens barrel 202. Naturally, the collision avoidance unit 204 protrudes to the optical disk 205 side from the lens effective surface 203.
Based on the above described configuration, even when the objective lens 201 approaches the surface of the optical disk 205, since the collision avoidance unit 204 softer than the surface of the optical disk 205 contacts the surface of the optical disk 205 prior to the lens effective surface 203, there is an advantage that scars on the surface of the optical disk 205 are reduced.
However, in the case of a configuration where the biaxial actuator is supported by elasticity of the four suspension wires in the optical heads device for selecting plural objective lenses and performing the reproduction or recoding of information from and to the optical disk of two or more different types having the transparent substrates different in thickness, the objective lens at the side not used for reproduction or recording of information may be moved by vibration or impact along with its movable portion. Therefore, the biaxial actuator is unable to be kept at a static position particularly under the circumstance, such as in a mobile application, where the external force is easy to be applied, and there may be the case that the biaxial actuator frequently collides with the optical disk by the movement, resulting in a damage to the optical disk or the objective lens. In the case where there is the possibility that the optical disk and the objective lens frequently collide in this way, it is necessary to reduce the collision itself of the collision avoidance unit for controlling the damage caused by the collision between the optical disk and the objective lens.
The present invention solves the above described conventional problems, and an object of the invention is to provide an optical heads device capable of avoiding the damage of the optical disk or the objective lens in the optical disk for selecting plural objective lenses and performing the reproduction or recording of information for the optical disk of two or more types having the transparent substrates different in thickness.